From d98d70f670297a4bfa86db1a67a9c024f7186f43 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Fri, 8 Dec 2023 15:16:04 +0200
Subject: [PATCH] cmd/utils, eth: disallow invalid snap sync / snapshot flag
 combos (#28657)

* eth: prevent startup in snap mode without snapshots

* cmd/utils: try to fix bad flag combos wrt snap sync and snapshot generation
---
 cmd/utils/flags.go | 10 ++++++++--
 eth/handler.go     |  4 ++++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 27e1b3f62..d4c918bf4 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -1677,10 +1677,16 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *ethconfig.Config) {
 	if ctx.IsSet(CacheLogSizeFlag.Name) {
 		cfg.FilterLogCacheSize = ctx.Int(CacheLogSizeFlag.Name)
 	}
-	if !ctx.Bool(SnapshotFlag.Name) {
+	if !ctx.Bool(SnapshotFlag.Name) || cfg.SnapshotCache == 0 {
 		// If snap-sync is requested, this flag is also required
 		if cfg.SyncMode == downloader.SnapSync {
-			log.Info("Snap sync requested, enabling --snapshot")
+			if !ctx.Bool(SnapshotFlag.Name) {
+				log.Warn("Snap sync requested, enabling --snapshot")
+			}
+			if cfg.SnapshotCache == 0 {
+				log.Warn("Snap sync requested, resetting --cache.snapshot")
+				cfg.SnapshotCache = ctx.Int(CacheFlag.Name) * CacheSnapshotFlag.Value / 100
+			}
 		} else {
 			cfg.TrieCleanCache += cfg.SnapshotCache
 			cfg.SnapshotCache = 0 // Disabled
diff --git a/eth/handler.go b/eth/handler.go
index f0021e564..a327af611 100644
--- a/eth/handler.go
+++ b/eth/handler.go
@@ -178,6 +178,10 @@ func newHandler(config *handlerConfig) (*handler, error) {
 			log.Info("Enabled snap sync", "head", head.Number, "hash", head.Hash())
 		}
 	}
+	// If snap sync is requested but snapshots are disabled, fail loudly
+	if h.snapSync.Load() && config.Chain.Snapshots() == nil {
+		return nil, errors.New("snap sync not supported with snapshots disabled")
+	}
 	// Construct the downloader (long sync)
 	h.downloader = downloader.New(config.Database, h.eventMux, h.chain, nil, h.removePeer, h.enableSyncedFeatures)
 	if ttd := h.chain.Config().TerminalTotalDifficulty; ttd != nil {